What's the big deal? It's the little things

The way small causes yield huge effects is itself only one piece of the much grander idea of simplexity, a science that is increasingly being studied at universities and institutes around the world, but nowhere more intensely than at the Santa Fe Institute in New Mexico. The institute was created in 1984 with Murray Gell-Mann -- the winner of the 1969 Nobel Prize in physics -- as its founding director. It's grown into a multidisciplinary think tank where dozens of researchers from fields as diverse as economics, chemistry, physics, sociology and neuroscience study the simple rules that undergird pretty much everything.

It's there that investigators are discovering how individual investors in a millions-strong stock market mirror the behavior of individual particles in an atomic collider, allowing software designers to write better programs that can help us understand both. It's there that scientists are exploring how cars on a highway or people fleeing a burning building mimic the motion of flowing water, and seeing if that can lead to safer roads or more evacuation-friendly office towers.

No single unified rule governs all complex or simple systems, but there are a few big ones. There's the concept of phase changes: In the same way that water flips its state from liquid to vapor at 212 degrees Fahrenheit, so too does a stressed geological fault flip from quiescence to quake when it shifts one centimeter too far, or a crowd explodes into a riot when a single bottle is thrown. There's the concept of relaxation pathways, which models the way rivulets become rivers simply by flowing downhill, or how oceans give up their excess heat by blasting it into the sky as fuel for a hurricane. Understand these simple concepts and you understand the foundations of the larger sciences.

The most powerful of the simplexity concepts, however, is choke points -- the keyholes in complex systems that can sometimes shut them down entirely. The London cholera epidemic of 1854, which could have claimed thousands of lives, was stopped cold when physician John Snow traced the contagion to a single contaminated water pump on Broad Street. The complex epidemic collided with the simple fix of shutting down the pump, and the simple fix won.